1. Field of the Invention
This invention relates to a process for preparing 1,5- and 1,8-dinitroanthraquinones with high purity, and to a process for the separation thereof into each component.
2. Description of the Prior Art
1,5- AND 1,8-DINITROANTHRAQUINONES ARE IMPORTANT INTERMEDIATES FOR PRODUCING DISPERSED DYES OF ANTHRAQUINONE SERIES OR THRENE DYES. That is, 1,5- and 1,8-dinitroanthraquinones can be converted into 1,5- and 1,8-diaminoanthraquinones by reduction, or can be converted to 1,5-dinitro-4,8-dihydroxyanthraquinone and 1,8-dinitro-4,5-dihydroxyanthraquinone, respectively, by phenoxylation, nitration and hydrolysis. Furthermore, these can be converted into the corresponding diaminodihydroxyanthraquinones by reduction. Also, 1,5- and 1,8-dihydroxyanthraquinones can be obtained by methoxylation and subsequent hydrolysis of 1,5- and 1,8-dinitroanthraquinones.
These various intermediates are extremely important as the intermediate compounds for the production of dispersed dyes and threne dyes. These intermediates have so far been synthesized solely via 1,5- and 1,8-anthraquinonedisulfonic acids. As is well known; a mercury catalyst is required in order to introduce sulfonic groups into .alpha.-positions of anthraquinone by sulfonation and, as the result, the recovery of the slight amount of mercury contained in the waste liquor or the intermediate increases the cost of the conventional process for preparing the intermediates via anthraquinonedisulfonic acids. However, it is difficult to completely remove mercury even with the utmost efforts.
Therefore, since the process via dinitroanthraquinone does not require the addition of mercury, the mercury-removing equipment is not necessary in such process and thus the cost for preventing environmental pollution can be greatly alleviated or completely reduced. However, in the conventionally known method of dinitration of anthraquinone, .beta.-isomers are produced as by-products in a large proportion which reduces the purity of the product to such an extent that the product does not possess the quality fit for the practical use as it is, and that further purification is required. Thus, the yield is seriously reduced, and the conventional process has not been commercially conducted in view of the complicated and inefficient operation in the purification step. Therefore, the conventional process has not yet been practically realized in industry.
That is, the dinitration reaction of anthraquinone has heretofore been studied by many investigators, and the results of the studies have been disclosed in patents or experimental reports. For example, a process comprising adding dropwise the mixed acid (a mixture of nitric acid and sulfuric acid) onto anthraquinone in 100% sulfuric acid and heating at 80.degree. C for 5 hours and at 125.degree. C for 2 hours, a process comprising heating at 95.degree. C for 2 hours in 96% sulfuric acid using mixed acid, and a process comprising heating at 100.degree. C for 10 hours in 20% fuming sulfuric acid, are described in Helv. Chem. Acta. 14,1404 (1931), U.S. Pat. No. 2,607,782 (1952) and PB report 82,232, p. 929, respectively. In any of these processes, however, a large amount of .alpha.,.beta.-dinitroanthraquinones and .beta.,.beta.-dinitroanthraquinones, i.e., 1,6-, 1,7-, 2,6-, or 2,7-dinitroanthraquinones which are not so valuable as the dyestuff intermediates are produced as by-products in addition to .beta.,.beta.-dinitroanthraquinones, i.e., 1,5- and 1,8-dinitroanthraquinones, resulting in poor yield. For example, it is disclosed in U.S. Pat. No. 2,607,782, that 1,5- and 1,8-dinitroanthraquinones are obtained by adding dropwise the mixed acid to a solution of anthraquinone in 96% sulfuric acid at temperatures ranging from 30.degree. to 70.degree. C, conducting the reaction at 95.degree. C for 2 hours, cooling the reaction mixture to 30.degree. C, separating the precipitates formed by filtration, washing them with 78% sulfuric acid then with water, and drying then the purity of 1,5- and 1,8-dinitroanthraquinones is as low as 65.8% and the yield is 87.3%. In addition, though the product is obtained in 97% yield by pouring the above-mentioned reaction solution into ice-water to precipitate, the purity is extremely low as 57.6% in total content. The other publicly known processes provide similar results.
Also, as the method for separating the resulting 1,5- and 1,8-dinitroanthraquinones from each other, there is a description in Helv. Chem. Acta. 14, 1404 - 27 (1931), in which it is reported that, after dinitration in 100% sulfuric acid, 1,5-dinitroanthraquinone is obtained by filtration and 1,8-dinitroanthraquinone is obtained by diluting the filtrate up to 70% with water. However, it is confirmed that, first of all, the separation of isomers is so incomplete that 20 - 30% of 1,8-dinitroanthraquinone is contained in 1,5-dinitroanthraquinone while .beta.-isomers as well as 1,5-dinitroanthraquinone are contained in 1,8-dinitroanthraquinone, and thus the purity of 1,8-derivative is as low as less than 50%. In addition, the filtration rate of the reaction mixture is too slow to be practically conducted, and hence this method possesses no practicality with consideration of the filtration property alone.